getPayload returns the payload used for effort compensation
 
    This method returns the specified payload mass at the
    end-effector that gets used to calculate efforts to
    compensate for gravitational effects and joint
    accelerations.
    
    Example
        mass = 0.1; % [kg]
        kin.setPayload(mass, 'CoM', com);
        mass = kin.getPayload(); % [kg]